Field of the Invention
The present invention relates to a controller for an injection molding machine.
Description of the Related Art
In injection molding, a step of moving a movable platen forward to close molds is divided into a mold closing step and a mold clamping step. The mold closing step is a step of moving the movable platen forward in a mold closing direction to cause a movable-side mold and a fixed-side mold to touch each other. Furthermore, the mold clamping step is a step executed after the mold closing step to move the movable platen further forward from the mold touch position to exert a predetermined mold clamping force.
An operation in which mold clamping and injection are carried out at the same time to reduce cycle time is conventionally known (Japanese Patent Application Laid-Open No. 2006-15527, Japanese Patent Application Laid-Open No. 7-256722, and Japanese Patent Application Laid-Open No. 8-90621). Furthermore, such a simultaneous operation of mold clamping and injection is known to be useful for avoiding inappropriate molding such as a “burn”. FIG. 6 is a diagram illustrating operation timings for the conventional mold clamping and injection steps.
When a resin is injected into a cavity of a mold while gas remains in the cavity, the gas is compressed by the resin that has entered the cavity as a result of the injection. The temperature and pressure of the gas are thus increased to cause a “burn” in a molded article. The use of the simultaneous operation of the above-mentioned mold clamping and injection is effective for suppressing a possible “burn” because a high mold clamping force is not exerted in the injection step of filling the cavity with the resin, so that the gas is easily vented from the molds through a small gap between the molds.
Japanese Patent Application Laid-Open No. 7-256722 discloses that, after the mold clamping step is started, a start timing for the injection step is set based on a delay time from the mold touch (time T1 in (1) in FIG. 6). However, in this setting method, as the injection step is started after the mold clamping step is started, the effect that facilitates venting of the gas from the molds through the gap is limited.
To further improve the gas venting, a method may be used in which, after the mold closing step is ended at the mold touch position, injection is immediately started, while the start of the mold clamping step is delayed. However, performing this operation needs setting of the delay time from the mold touch in the mold closing step until the mold clamping step is started (time T2 in (2) in FIG. 6).
Thus, in the related art, when operating conditions for an injection molding machine are set so as to allow a reduction in cycle time and gas venting to be achieved, the delay times T1 and T2 depicted in FIG. 6 are needed to be set based on the start timings for the mold clamping step and the injection step. An operator who sets the operating conditions for the injection molding machine needs to set each of the delay times (T1 or T2). Consequently, the setting is disadvantageously complicated.